1. Field of the Invention
The present invention relates to an adhesive resin composition which is utilized as an adhesive material between layers of a multi-layer laminate. Scrap or waste material from the adhesive resin or from the multi-layer laminate can be recycled as an adhesive resin composition.
2. Description of the Related Arts
In recent years, resin containers having the gas barrier property have been widely used in place of metal containers, particularly in the area of food containers. The resin containers have the advantage of good appearance, cleanness, light weight and good productivity which are lacking in metal containers.
The resin containers having the oxygen gas barrier property are prepared by molding multi-layer laminates or multi-layer sheets formed by laminating a resin having the oxygen gas barrier property, such as polyamide resins (sometimes abbreviated to "PA" hereinafter), polyvinylidene chloride copolymer resins and saponified products of ethylene-vinyl acetate copolymers (sometimes abbreviated to "EVOH" hereinafter), to polyolefin resins. The multi-layer laminates are generally prepared by forming an adhesive layer of various kinds of adhesive resins between the layers because adhesion between the resin having the oxygen gas barrier property and the polyolefin resin is generally poor.
When PA is used as the resin having the oxygen gas barrier property, polyolefin resins modified with an acid anhydride, such as maleic anhydride, are generally used as the adhesive resin. Blends of olefin resins with a copolymer of an .alpha.-olefin and an .alpha.,.beta.-unsaturated carboxylic acid or an ester thereof, a polyolefin resin modified by grafting of an .alpha.,.beta.-unsaturated carboxylic acid, an ionomer resin obtained by ionizing a copolymer of ethylene and methacrylic acid or an ester thereof with sodium, zinc, magnesium or the like or an ethylene-propylene-diene rubber modified with maleic anhydride have also been proposed as the adhesive resin.
When EVOH is used as the resin having the oxygen gas barrier property, resins obtained by grafting or copolymerization of an unsaturated carboxylic acid, an acid anhydride or an ester monomer to a polyolefin resin are used as the adhesive resin U.S. Pat. Nos. 4,026,967 and 3,953,655, Japanese Patent Application Laid-Open No. 98784/1976 and Japanese Patent Publication Nos. 15423/1969 and 4822/1974).
When containers are formed by molding from the multi-layer laminate or the multi-layer sheet, a considerable amount of scrap material is formed. The amount of the scrap material is 40% in some molding methods. Utilization by recycling of the waste plastics is urged by the society for protection of resources on the earth.
Because of this social requirement, improvement of the overall recycling of the utilized materials by addition of the adhesive resins described above as a compatibilizer is under investigation with some resin compositions and in the production of molded products from the resin compositions.
However, the method of recycling for reuse by addition of the adhesive resins as described above have problems that interlayer strength is decreased to a great extent to cause separation of the layers and that gel is formed and yellow discoloring occurs because of the unreacted monomer for the modification remaining in the adhesive resin.